Blades and vanes for land-based power generation and for aerospace applications are typically formed from superalloy materials. The term “superalloy” is used herein as it is commonly used in the art to refer to a highly corrosion-resistant and oxidation-resistant alloy that exhibits excellent mechanical strength and resistance to creep even at high temperatures. Superalloys typically include a high nickel or cobalt content. Exemplary superalloys include, but are not limited to, alloys sold under the trademarks and brand names Hastelloy, Inconel alloys (e.g. IN 738, IN 792, IN 939), Rene alloys (e.g., Rene N5, Rene 41, Rene 80, Rene 108, Rene 142, Rene 220), Haynes alloys, Mar M, CM 247, CM 247 LC, C263, 718, X-750, ECY 768, 262, X45, PWA 1483 and CMSX (e.g. CMSX-4) single crystal alloys, GTD 111, GTD 222, MGA 1400, MGA 2400, PSM 116, CMSX-8, CMSX-10, PWA 1484, IN 713C, Mar-M-200, PWA 1480, IN 100, IN 700, Udimet 600, Udimet 500 and titanium aluminide.
Since the development of superalloy materials, various strategies have been employed to provide mechanical strength to the materials to improve the lifetimes thereof. Some elements can provide strength in solid solution. Examples include tantalum, tungsten and rhenium. Carbide precipitations can also add to strength. Elements forming carbides include titanium, tantalum, hafnium and niobium. Most particularly, superalloy materials may be strengthened through the formation of a precipitate phase known as gamma prime (γ′). This phase has the basic composition Ni3(Al,Ti). If properly sized and of sufficient volume fraction, this phase offers significant strengthening—most particularly to nickel based superalloys. Some superalloys are also strengthened by another precipitate known as gamma double prime. This precipitate is of the composition Ni3Nb, and is important for strengthening some nickel and nickel/iron-based superalloys. Gamma prime phases have an ordered crystalline lattice, which aids in providing added strength to the material. In addition, single crystal solidification techniques have been developed for superalloys that enable grain boundaries to be entirely eliminated from a casting, as well as increase the volume fraction of the γ′ precipitates. Alternatively, superalloys may be directionally solidified so as to include only longitudinally directed grains for added strength.
Generally, superalloy materials are among the most difficult materials to weld due to their susceptibility to weld solidification cracking and strain age cracking under the conditions (e.g., high temperature) necessary to weld and heat treat such materials. Further, when cladding on a superalloy material, it is appreciated that unless additional steps are taken, the cladding may not have the same physical properties, e.g., mechanical strength, as the underlying substrate.